1. Field of the Invention
The present invention relates to a radiographic imaging device, a radiographic imaging method, and a computer readable medium storing a radiographic imaging program. The present invention relates particularly to a radiographic imaging device, a radiographic imaging method, and a computer readable medium storing a radiographic imaging program, for imaging a medical radiographic image.
2. Description of the Related Art
Conventional radiographic imaging devices that perform radiographic imaging for medical diagnostic purposes, have been known. In such a radiographic imaging device, radiation irradiated from a radiation irradiation device and that has passed through an investigation subject is detected, and a radiographic image is imaged. In such a radiographic imaging device, radiographic imaging is performed by collecting and reading out charges generated according to the irradiated radiation.
Such a radiographic imaging device is provided with a radiation detection element for detecting radiation. The radiation detection element generates charges when irradiated either with radiation or with light that has been converted from the radiation. In the radiographic imaging device, the electrical signals corresponding to the generated charges is amplified in an amplification means before performing radiographic image read out (imaging).
The amplification factor for amplifying the electrical signals in the amplification means is set according to the magnitude of the electrical signals. Namely, the amplification factor of the amplification means is set according to the radiation dose irradiated (or the illumination amount of light converted from radiation).
Japanese Patent Application Laid-Open (JP-A) No. 2009-219538 discloses a technology that sets the gain of an amplification circuit when reading out the charges based on the radiation dose irradiated. In this technology, a current detection means is provided separately to an image detection circuit for detecting current flowing in a bias line for supplying a reverse bias voltage to a photoelectric conversion device.
Further, JP-A No. 2008-212644 discloses a technology for controlling an amplification factor in a read-out means, based on X-ray dose detected by a radiation monitor, such that a desired SN ratio is obtained in the image signal.
In the technology of JP-A No. 2009-219538, the circuit (device) size may be increased since the current detection means needs to be provided in the bias power source output section, in addition and separate to the image detection circuit. Namely, this technology may be difficult to implement in a small size and lightweight device such as a Flat Panel Detector (FPD) cassette. Furthermore, when the substrate is split into plural regions with gain set for each of the regions, higher precision detection is required to set gain appropriate to a relevant region for imaging an investigation subject, due to low charge amounts to be detected. A large scale detection circuit is required for performing high precision detection, resulting in the size of the device increasing. Furthermore, since the current detection means is provided at the bias power source, the supply current fluctuates according to the radiation dose irradiated, and may cause image noise.
In the technology disclosed in JP-A No. 2008-212644, the X-ray dose is detected by using a radiation monitor such as an Automatic Exposure Control device (AEC). Accordingly, a radiation monitor separate to a flat panel detector is required, and this may lead to increase in a device size. Further, the increase in size of the device may lead to increase of power consumption, and increase in the number of components. Furthermore, since the mechanism for detecting the radiation with the flat panel detector is different from the mechanism for detecting radiation with the radiation monitor, discrepancies arise in light exposure amounts detected depending on the irradiation conditions due to the sensitivity changing between the two detection systems when the X-ray irradiation dose (irradiation energy) changes.